There have been conventionally proposed various techniques for preventing a decrease of data transfer efficiency even with a change in a line state (line quality) during data communication (see, for example, Patent Documents 1 and 2).
Patent Document 1 discloses a data transfer method of determining a length of a frame to be transmitted next based on a success or failure state of frame transmission.
Patent Document 2 discloses a technique for measuring an Ec/Io (pilot signal strength to total received signal strength) level of radio signals in wireless communication, determining whether a line state is recovering or worsening, setting the data size of one packet based on the result of determination, and holding communication.